base-files: execute package's "postinst" after executing uci-defaults

Allow "postinst" scripts to perform extra actions after applying all
kind of fixups implemented using uci-defaults.

This is needed e.g. by uhttpd-mod-ubus which after installation in a
running systems needs to:
1. Update uhttpd config using its uci-defaults script
2. Reload uhttpd

While this approach makes sense there is a risk it'll blow up some
corner case postinst usages. There is only 1 way to find out.

Cc: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
(cherry picked from commit b799dd3c70)

package/base-files/files/lib/functions.sh

@@ -262,11 +262,6 @@ default_postinst() {
 
 	add_group_and_user "${pkgname}"
 
-	if [ -f "$root/usr/lib/opkg/info/${pkgname}.postinst-pkg" ]; then
-		( . "$root/usr/lib/opkg/info/${pkgname}.postinst-pkg" )
-		ret=$?
-	fi
-
 	if [ -d "$root/rootfs-overlay" ]; then
 		cp -R $root/rootfs-overlay/. $root/
 		rm -fR $root/rootfs-overlay/
@@ -292,6 +287,11 @@ default_postinst() {
 		rm -f /tmp/luci-indexcache
 	fi
 
+	if [ -f "$root/usr/lib/opkg/info/${pkgname}.postinst-pkg" ]; then
+		( . "$root/usr/lib/opkg/info/${pkgname}.postinst-pkg" )
+		ret=$?
+	fi
+
 	local shell="$(command -v bash)"
 	for i in $(grep -s "^/etc/init.d/" "$root$filelist"); do
 		if [ -n "$root" ]; then